In earth-related space or aircraft flight operations, it is frequently necessary and desirable to determine the sun angle relative to the horizon at any given place and time on earth. For example, this is a necessary determination in planning for aerial photography. Heretofore, the sun angle could be calculated manually using celestial navigational methods and solar ephemeris data or by using a computer program. These methods are disadvantageous in the amount of reference data, time and equipment required to perform a sun angle calculation.